NAVAL POSTGRADUATE SCHOOL
Monterey, California
THESIS
INEXPENSIVE GLOBAL
LOCATION AND TRACKING SYSTEMS
USING GEOSTATIONARY SATELLITES
Danny L. DeFries
June 1989
Thesis Advisor
Tri T. Ha
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Title (include secuntv classification) INEXPENSIVE GLOBAL LOCATION AND TRACKING SYSTEMS USING
EOSTATIONARY SATELLITES
) Danny L. DeFries
Ja Type of Report
Iaster's Thesis
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June 1989
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> Supplementary Notation The views expressed in this thesis are those of the author and do not reflect the official policy or po
tion of the Department of Defense or the U.S. Government.
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IS Subject Terms (continue on reverse if necessary and identify by block n
Geostationary Satellite Navigation, position determination.
) Abstract (continue on reverse if necessary and identify by block number)
Inexpensive Global Location and Tracking Systems are currently being designed to provide the civilian market lowcost
idio position determination. This paper discusses two possible designs. The first design employs 3 or 4 satellites, depending
n whether altitude is known a priori, each transmitting continuous ranging signals. The user transceiver receives the ranging
gnals. measures the time differentials of the receipt of the signals and transfers this information to a control station via a
itellite link. The control station computes the user position from this data and sends the position coordinates back to the
ser via another satellite link. In the second design, each user transceiver transmits a unique code to the control station via
le 3 or 4 satellite links, again depending on whether the altitude is known a priori. The control station measures the time
ifferentials of the receipt of the signals and determines the user position. This position information is then transmitted back
5 the user via a satellite link.
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Inexpensive Global
Location and Tracking Systems
Using Geostationary Satellites
by
Danny L. De Fries
Major, United States Army
B.S., University of South Dakota, 1975
Submitted in partial fulfillment of the
requirements for the degree of
MASTER OF SCIENCE IN ELECTRICAL ENGINEERING
from the
NAVAL POSTGRADUATE SCHOOL
June 1989
ABSTRACT
Inexpensive Global Location and Tracking Systems are currently being designed to
provide the civilian market lowcost radio position determination. This paper discusses
two possible designs. The first design employs 3 or 4 satellites, depending on whether
altitude is known a priori, each transmitting continuous ranging signals. The user
transceiver receives the ranging signals, measures the time differentials of the receipt of
the signals and transfers this information to a control station via a satellite link. The
control station computes the user position from this data and sends the position coor
dinates back to the user via another satellite link. In the second design, each user
transceiver transmits a unique code to the control station via the 3 or 4 satellite links,
again depending on whether the altitude is known a priori. The control station measures
the time differentials of the receipt of the signals and determines the user position. This
position information is then transmitted back to the user via a satellite link.
U'l^
TABLE OF CONTENTS
I. INTRODUCTION 1
II. SYSTEM I 5
A. SYSTEM I DESCRIPTION 5
B. SATELLITETOUSER DOWNLINK 5
1. Downlink Frequency and Bandwidth 5
2. PseudoNoise (PN) Ranging Code 6
C. USERTOCONTROL STATION LINK 7
1. Uplink Bandwidth 7
2. UsertoControl Station Data 9
3. SatellitetoControl Station Downlink 13
D. POSITION DETERMINATION 13
E. POSITION ERROR 19
F. CONTROL STATIONTOUSER DATA LINK 23
1. Uplink Bandwidth 23
2. Control StationtoUser Data 24
3. SatellitetoUser Downlink 25
III. SYSTEM II 26
A. SYSTEM II DESCRIPTION 26
B. USERTOCONTROL STATION LINK 27
1. Uplink Bandwidth 27
2. UsertoControl Station Data 27
3. SatellitetoControl Station Downlink 28
C. POSITION DETERMINATION 28
D. CONTROL STATIONTOUSER DATA LINK 29
1 . Uplink Bandwidth 29
2. Control StationtoUser Data 30
3. Satellite to User Downlink 30
IV. SYSTEM COMPARISONS AND CONCLUSIONS 32
V. LIST OF REFERENCES 33
VI. INITIAL DISTRIBUTION LIST 34
LIST OF TABLES
Table 1. SYSTEM I USERTOCONTROL STATION LINK ANALYSIS . .
Table 2. NUMBER OF SIMULTANEOUS CDMA CHANNELS WITH FEC
Table 3. NUMBER OF SIMULTANEOUS CDMA CHANNELS WITH FEC
Table 4. NUMBER OF SIMULTANEOUS CDMA CHANNELS WITH FEC
Table 5. NUMBER OF SIMULTANEOUS CDMA CHANNELS WITH FEC
Table 6. SYSTEM I CONTROL STATIONTOUSER LINK ANALYSIS . .
Table 7. SYSTEM II USERTOCONTROL STATION LINK ANALYSIS . .
Table 8. SYSTEM II CONTROL STATIONTOUSER LINK ANALYSIS . .
10
14
15
16
17
24
28
31
LIST OF FIGURES
Figure 1. Geocentric Coordinate System 2
Figure 2. Differential Distance Measurement 7
Figure 3. Data Frame (User to Control Station) 11
Figure 4. TDM Frame (Control Station to Users) 25
I. INTRODUCTION
Today, the United States Department of Defense (DOD) is utilizing the XAVSTAR
Global Positioning System (GPS) for accurate position determination. GPS employs 18
geosynchronous satellites within 6 different orbits with 3 satellites in each orbit. GPS
provides highly accurate position determination to an unlimited number of users world
wide, although the position determination accuracy provided to the civilian community
is intentionally degraded due to national defense reasons. The degraded mode still ena
bles the civilian community to attain accuracies of 100 meters.
In addition to the high number of operational satellites that are required to support
the 24hour worldwide GPS system, the user equipment cost is also quite high due to
its complexity. Even though the user equipment cost has decreased considerably since
GPS was first introduced, the civilian community can not afford the user equipment.
To lower the cost of the position determination system so that the civilian community
can afford to install position determination equipment in one's vehicle, a simpler system
has to be designed and the total number of satellites deployed has to be reduced.
This thesis presents two lowcost concepts of vehicle location and tracking using
geostationary satellites. The first concept is borrowed from the concept of geostationary
satellite navigation systems presented in [Ref. 1]. The second concept is a new concept
that is presented in this thesis. For the systems to be utilized by the civilian community,
the systems have to be lower in cost than GPS, provide reasonable position accuracy,
and be reliable. To cover the United States, each system requires four satellites to de
termine longitude, latitude, and altitude, or three satellites if altitude is not measured.
Like the geostationary satellite navigation system, the location and tracking systems will
also deploy three or four geostationary satellites parked in orbits on the equator at a
latitude of zero degrees and altitude of approximately 35,786 kilometers. The difference
between the proposed location and tracking system and the geostationary navigation
system is that the location and tracking system user does not determine his position but
relies on the central control station to determine it. The satellites continuously and
synchronously transmit a satelliteunique ranging code to the user on earth. The user
receives the satellites signals at different times due to the path length differences between
the user and each of the satellites. The transceiver measures the time differentials be
tween a designated signal and the remaining signals and transmits this information to a
control station via a satellite communications link. The control station calculates the
user position from the time differentials and transmits the user coordinates to the user
via another satellite channel. By placing the computational burden on the central con
trol station, the location and tracking transceiver can be made at a lower cost.
Position determination in a geostationary coordinate system is normally defined in
a geocentric coordinate system as shown in Figure 1. The xaxis is the intersection of
the equator plane (0° latitude) and the Greenwich meridian plane (0' longitude) and is
oriented from the center of the earth, the zaxis is the polar axis oriented from south to
north, and the yaxis completes the righthanded Cartesian coordinate system. We des
ignate the unknown user position by (x,y,z), the known positions of n = 3 or 4
geostationary satellites by (x t ,y n z,) where /= 1, 2, ..., n, and the known position of the
central control station by (.r ..)'o, z ).
O'Longiludo
Figure 1. Geocentric Coordinate System: (Ref. 1]
The main function of the transceiver is to measure the differential distance
fl . = d x d b i= 1,2,..., n (1)
representing the differences in the distance to the user from one satellite, arbitrarily
designated as satellite one, and from each of the other satellites. The variable a, repres
ents the difference in the distance of satellite one to the user and that of each of the other
satellites to the user. The variable d, represents the distance from each satellite to the
user. The differential distance determination concept is discussed later. The squared
distance from the user position to each geostationary satellite can be expressed by
4 = (x  a) 2 + (y yf + (z  zf, f=l,2, ..., n (2)
where (x,y, z) represent the users coordinate position in the Cartesian coordinate system
and {x t ,y,. z,) represents each of the satellites' positions.
For n = 4. (1) and (2) combine to form a set of four independent equations and four
unknowns, namely, x, y. z, and d x . These four equations are
(rf,  af = (x  xf + Cv })) 2 + (z  z t ) 2 , 1=1,2, ..., 4 (3)
which can be solved using the measured data a, and the known satellite ephemeris
(x,.y,. z), i = 1. 2. 3, 4. The value a, is found through the use of a correlation register and
ranging codes which will be discussed later. A detailed discussion of the concept can be
found in[Ref. I].
For the three satellite system, n = 3, we use
. v 2 + / + 2 2 = (£ + /*) 2 (4)
where R = 6378 km is the Earth's mean equatorial radius, and h is the user altitude
(assumed to be known), as the fourth equation in addition to the three equations
(4  a y = (x  x,y + Cv  y,y + (z  z,y /= 1,2,3.
The first system requires each satellite to broadcast a unique pseudonoise (P\)
code in the frequency band 24S3.5  2500 MHz. The PX codes are selected from a set
of Gold codes which allow minimum interference between signals from various satellites.
The satellites employ extremely stable onboard atomic clocks which are mutually syn
chronized. A central control station which can view all satellites is responsible for the
clock correction via a communications link in the frequency band 6526.5  6541.5 MHz.
The user transceiver measures the time differentials between one satellite arbitrarily
designated as satellite one, and each of the other satellites. The accuracy of the meas
urements and their effect on the user position determination accuracy will be discussed
later. The user transceiver then sends the measured time differentials to the central
control station for computing the user coordinates via a code division multiple access
(CDMA) uplink in the frequency band 1610  1626.5 MHz. The central control station
calculates the user coordinates using the received time differentials and the predicted
satellite ephemerides. It then relays the coordinates to the user via a time division mul
tiplexed (TDM) downlink in the frequency band 2483.5  2500 MHz.
The second system requires the user transceiver to broadcast a PN code to the cen
tral control station via a code division multiple access uplink. The central control sta
tion calculates the user differential distances to the satellites with the available satellite
ephemeris and then the user coordinates which are relayed to the user via the TDM
downlink.
II. SYSTEM I
A. SYSTEM I DESCRIPTION
The frequency assignment and bandwidth allocated for each of the satellite links
listed below are assigned by the Federal Communications Commission as listed in [Ref.
2J.
• SatellitetoUser Ranging Link
Frequency 2483.5  2493.73 MHz
Bandwidth 10.23 MHz
• UsertoControl Station
UsertoSatellite Uplink
Frequency 1610  1626.5 MHz
Bandwidth 16.5 MHz
SatellitetoControl Station Downlink
Frequency 5150  5166.5 MHz
Bandwidth 16.5 MHz
• Control StationtoUser
Control StutiontoSatellite Uplink
Frequency 6524.5  6530.77 MHz
Bandwidth 6.27 MHz
Satellite to User Downlink
Frequency 2493.73  2500 MHz
Bandwidth 6.27 MHz
• Control StationtoSatellite Command Link
Frequency 6526.5  6541.5 MHz
Bandwidth 15 MHz
B. SATELLITETOUSER DOWNLINK
I. Downlink Frequency and Bandwidth
The communications downlink from each of the satellites to the user occupies
a bandwidth of 16.5 MHz from 2483.5 to 2500 MHz. Within this bandwidth, the satel
lites must transmit a pseudonoise ranging code needed for user position determination
and provide the downlink for the control stationtouser data link. In System I design,
the satellites must employ two satellitetouser channels, one for the sole purpose of
transmitting the unique pseudonoise code and one to perform as a relay for the data
link from the control station to the user. The pseudonoise code will be transmitted
between the frequencies of 2483.5 and 2493.73 MHz in a bandwidth of 10.23 MHz. The
control stationtouser data link will be transmitted between the frequencies of 2493.73
and 2500 MHz in a bandwidth of 6.27 MHz.
2. PseudoNoise (PN) Ranging Code
The PN ranging code transmitted by the satellites is received by the user and is
used to determine time differentials. The accuracy of the measurements of the time dif
ferentials used to determine the user position is of prime importance to the overall po
sition accuracy. The more precise the time measurement is, the more accurate the
position determination will be. GPS uses code chip rates of 10.23 Mbit/s in its trans
missions to the user. For our example, a given code length of 2 19  1 = 524,287 chips
and a chip rate of 10.23 Mbit/s results in a code period of 524,287, 10.23 x 10 6 = 51.25
ms. A lower code length of 2 16 —1 = 65,535 and a lower chip rate of 1.023 Mbit/s has a
period of 65,535 1.023 x 10 6 = 64.06 ms and a larger error in the differential distance
measurement. The code tracking loop that would be used is able to maintain code
alignment to approximately 0.01 chip. This is a conservative figure, for code tracking
loops can be accurate to 0.001 chip. For a 0.01 alignment factor and a 10.23 Mbit/s chip
rate, a ranging error of 0.29 meter would exist, where a 1.023 Mbit s chip rate would
have a ranging error of 2.9 meters [Ref. 1]. To better understand the fundamentals of
PN ranging codes that determine position accuracy, Figure 2 shows the concept of dif
ferential distance measurement. To determine the differential distance, the user equip
ment must be able to perform a correlation operation among the satellites' codes and
internally stored copies of those codes. The receiver clock must be able to count the
number of chips between the correlation peak of the first received code and the subse
quent codes as shown in Figure 2. Since a, may not be an integer multiple number of
chips, the receiver may use the correlation value relative to the peak correlation voltage
to determine a fraction of a chip in the measurement. As was stated earlier, a fraction
of a chip of 0.001 can be measured.
 PN Code Period 
Figure 2. Differential Distance Measurement: [Ref. 1]
In [Ref. 1], the PN ranging code and its effects on position determination accuracy is
discussed in further detail.
C. USERTOCONTROL STATION LINK
1. Uplink Bandwidth
The frequency bandwidth allocated to the usertocontrol station data link is
16101626.5 MHz. The user direct sequence spreads the data with a Gold code of period
2 10  1 = 1023 chips which is a standard period for navigation systems. Thus for a
bandwidth of 16.5 MHz from 16101626.5 MHz, the typical user data rate is approxi
mately 16,129 bits s when spread at 1023 chips per bit, if Quaternary Phase Shift Keying
(QPSK) is used as a modulation scheme. That is, the chip rate is ( 16, 129)( 1,023) =
16.5 x 10 6 chips. With QPSK, there are 2 bits per symbol and hence the symbol rate is
S.5 x 10 6 symbols a second. The bandwidth required (double sideband for QPSK) is
twice the symbol rate or equal to 16.5 MHz which is compatible with the available 16.5
MHz bandwidth. The users must share this available bandwidth with each other to
transmit their IDs, time differentials, and other information to the control station.
The usertosatellite uplink is the most critical link in the system. The user is
not able to employ or utilize a high gain dish antenna like those used in the fixed
stations. The maximum output RF power is also limited by the power available in a
mobile vehicle. To calculate the Jiffective Isotropic Radiated Power (El RP) of a vehicle,
Eq. (5) is used, where P, is the transmitter power out and G t is the effective gain of the
antenna.
E1RP = P t G t (5)
In our design, a transmitter power out of 80 watts which is equal to 19 dBW and an
omni directional antenna with a gain of 4 dB will yield an EIRP of 23 dBW. These design
values are selected with some judgment and are also being used in current navigation
systems.
The Free Space Path Loss (FSPL) is calculated using Eq. (6).
FSPL(dB) = 10 log( ^ \ (6)
where/is the carrier frequency, */is the slant range, and c is the speed of light. At a slant
range of 35.786 km and a carrier frequency of 1618 MHz, a FSPL of approximately 190
dB is obtained.
A standard satellite G,'T of + 3 dB K has been chosen for this design model and
Boltzmann's constant k is given as 228.6 dBW/KHz. To calculate the uplink carrier
tonoise density ratio, Eq. (7) is used.
£■ {dB) = EIRP{dB\\ r )  FSPL{dB) + y {dbjK)  k{dBW!KHz) (7)
The EIRP of 23 dBW, FSPL of 190 dB, satellite GT of +3 dB K and Boltzmann's
constant of 228. 6 dBW KHz are entered into the Eq. (7), obtaining an uplink carrier
tonoise density ratio of 64.6 dBHz. This density ratio is sufficient to support the data
rate that the system requires for successful operation.
For the downlink, the same calculations are performed to obtain the downlink
carriertonoise density ratio. A FSPL of 198 dB is calculated for the carrier frequency
of 5150 MHz. A satellite EIRP of 36 dBW and a control station G/T of 20 dB K are
used to calculate the downlink carriertonoise density ratio. These values are standard
satellite EIRP and station G T values.
The total carriertonoise density ratio is calculated using Eq. (8) found in [Ref.
3].
(#)[(*):♦(#);]
To solve for the total carriertonoise density ratio, the values of the carriertonoise
density ratios must be converted to real numbers, substituted into Eq. (8), the equation
solved and the answer converted to the logarithm form of dBHz.
A margin of 2 dB is further engineered into the system design to allow for in
terferences that would degrade the operation of the system. The data rate is calculated
by subtracting the 2 dB margin from the total carriertonoise ratio, converting that dB
value to a factor and then dividing that factor by the equivalence of the required
signaltonoise ratio which is set to two representative values of 15 and 20 dB for this
system design. These required signaltonoise ratios are typical satellite navigation
signaltonoise ratios; each will be used for design calculations.
To calculate the data rate for a lower required signaltonoise ratio of 15 dB, the
2 dB margin is subtracted from the total carriertonoise ratio of 64.57 dBHz, giving
62.57 dBHz. This ratio is converted to a value of 1.807 x 10 6 and is divided by 31.26
(value of 15 dB) which in turn yields the data rate of approximately 57 kbps. When the
required signaltonoise ratio is increased to 20 dB (factor of 100), the data rate is low
ered to IS kbps. The link analysis is tabulated in Table 1.
2. UsertoControl Station Data
After receiving 3 or 4 satellites' ranging signals and measuring time differentials,
the user must transmit the information to the control station for calculation. The
transmission is Code Division Multiple Access (CDMA) as required by the Federal
Communications Commission (FCC) and is designed to provide the system with a bit
error probability of 10" 6 to 10"". (A bit error probability of 10~ 6 and 10"" provides the
reliability needed for a successful system.) The data stream must include a synchronous
code word in the user transmission for the control station to synchronize to the trans
mission. Once the the control station has synchronized itself to the data transmission.
the control station can identify the information that the user is sending to the control
station from within the data frame. A Barker code word of 13 bits would provide the
synchronization that the control station equipment requires and enable the control sta
tion to lock on to the transmission and recover the user transmitted data [Ref. 4].
Other information that is sent includes the user ID, the ID of the satellite that
was received first, the second and third satellites IDs and the time differentials AT in
symbols between receipt of the signals of the satellites. These time differentials are de
termined by the correlator. The minimum distance that a satellite may be from the user
is 35,786 km which corresponds to a minimum propagation delay of 119.287 ms. The
maximum distance is 41.678.82 km which corresponds to the maximum propagation
Table 1. SYSTEM I USERTOCONTROL STATION LINK ANALYSIS
Uplink Frequency
1618 MHz
Antenna Gain
4dB
Transmitted Power
80 W
Carrier EIRP
23 dBW
Free Space Path Loss
190 dB
Satellite G T
+ 3 dB K
Boltzmann's Constant
228. 6 dBW KHz
Uplink
CarriertoNoise
Density Ratio
64.6 dBHz
Downlink Frequency
5150 MHz
Satellite EIRP
36 dBW
Free Space Path Loss
198 dB
Control Station G T
20 dB K
Downlink
CarriertoNoise
Density Ratio
86.6 dBHz
Total
CarriertoNoise
Density Ratio
64.57 dBHz
Margin
2dB
If required rr =
15 dB
20 dB
Then Data Rate can be
57 kbps
18 kbps
delay of 138.929 ms. A maximum time differential between the minimum and maximum
time delays is 19.642 ms. We require an accuracy of 0.1 /j.sec. This allows a quantization
interval of 0.2 ,usec. The number of 0.2 /isec intervals in 19,642 /isec is 98,210. To rep
resent this value, 2 18 = 262,144 will easily suffice to represent the maximum time differ
ential. Thus there are 18 bits required to represent the maximum differential time
measurement between the first satellite and each of the other satellites and 2 additional
bits to identify the satellite for a total of 20 bits used. In the threesatellite design, the
altitude of the user must also be transmitted to the control station for position determi
nation. An altitude of 100,000 meters with 0.1 meter accuracy can be represented with
20 bits. For the foursatellite case, the field for altitude is used for satellite 4 ID and
differential time measurement. In all cases, 20 bits for additional information are de
signed into the frame for future uses such as emergency reporting of position location
when the user may be in need of it. See Figure 2 for an example of a data frame.
111 BITS
1 3
16
2
20
20
20
20
4 ►
^ ►
<« ►
ALTITUDE
SYNC
USER
I D
SAT 1
I D
S A T
1 D &
2
D T
SAT
I D &
3
D T
SAT 4
1 & D T
GENERAL
INFORMAT ION
Figure 3. Data Frame (User to Control Station)
To increase the number of channels that could exist on the system, Forward
Error Correction (FEC) is used. The use of FEC lowers the required signaltonoise
ratio and thus allows more CDMA channels to be used. A convolution code with
Viterbi decoding and soft decision will increase the total number of channels [Ref. 5].
There are various combinations of convolution code rates and constraint lengths that
can be examined to provide the optimum data rate for the system.
To calculate the number K + 1 of CDMA channels that can successfully exist
within the bandwidth at a bit error probability of 10 6 and 10~ 7 , the following results
from Refs. 5 and 6 were used. To calculate the number K+ 1 of CDMA channels that
can be succesfully utilized simultaneously, Eq. (9) is used.
A' =3 A"
_Ao_
2E h
(9)
The chips per bit (N), the design bit energytonoise ratio I rr 1 and the bit energy
tonoise plus user interference density ratio ( — ) must be known to solve for K. For
reliability, bit energytonoise ratios of 15 and 20 dB were selected for the system. The
chips per bit (N) is 1023. The value for the bit energytonoise plus user interference
density ratio is a function of other parameters as follows.
/mS.)
where Q{x) is defined as
ew
e~du (11)
The code rate (R) and the channel transition probability (p) must be known to calculate
the energytonoise plus user interference density ratio. A code rate (R) of 1,2 to 7,8
was used in the calculations to determine the bit rate that will support the maximum
number of CDMA channels. The probability (p) is a function of parameters that are
determined by the code rate and system design. To calculate p, Eq. 12 is used [Ref. 6].
P b ,code d <J \J df "'P 2 (12)
For System 1 design, coded bit error probabilities (P btCCded ) of 10~ 6 and 10" 1 are
used to insure a reliable system for the user. The number k of encoder input bits and
the number n of encoder output bits establish the code rate (R), where R = —. The
variable B d used to calculate the channel transition probability (p) is a calculated value
that is determined by the code rate, constraint length, and the free distance of the code.
The variable d fret is the free distance of the convolutional code and is determined by the
code rate and the constraint length. The values B d and d /r „ have been previously cal
culated in [Refs. 5,6] at a constraint length of 7 for the code rates of 1/2 to 7 8.
To calculate the number of simultaneous CDMA channels that the system can
support, the channel transition probability (p) must be found with Eq. (12). The number
k of encoder input bits. B d , d,,„ and the coded bit error probability (P byCOded ) are entered
into Eq. (12) to solve for the channel transition probability (p). Then the bit energy
tonoise plus user interference density ratio ( ~ ) is substituted into Eq. (10) along
with the given chips per bit (N) of 1023, and the design bit energytonoise density
ratio rr J of 15 and 20 dB. In Tables 2 and 4, the number K+ 1 of channels that can
successfully be used with hard decision Viterbi coding at a bit error probability of 10 6
and 10 _ " respectively are shown. For example, given the code rate (R) of 1/2, the en
coded bit k is 1, B d is 36, and d fr „ is 10. For a P btCOded of 10~ 6 a channel transition
probability (p) of .00703 is calculated. With a p of .00703 and a code rate (R) of 1/2, a
bit energytonoise plus user interference density ratio ( ^ \ of 5.87 is calculated. This
value, the chips per bit (N) of 1023, and the design energytonoise density ratio of 20
dB (100) yields a value K of 246. The number of channels K+ 1 is then 247. An in
spection of the tables reveals that a code rate of 1/2 yields the largest number of simul
taneous channels that can be used successfully. When soft decision Viterbi coding is
used, a decrease in the bit energytonoise plus user interference density ratio of 2 dB is
realized. Thus soft decision Viterbi coding further increases the number of CDMA
channels that can be used which is shown in Tables 3 and 5 for 10 6 and 10 _ " respectively.
The different bit error probabilities of 10~ 6 and 10"' and soft and hard Viterbi decisions
are used in the calculations to provide the reader an indication of four possible system
capabilities.
The major limitation in using lower code rates of 1/2 is that the bandwidth of
the system that is available to the user is severely reduced. Although the number of
CDMA simultaneous channels is greatly increased, the bandwidth of the system is de
creased. Further research is required in the area of the coding techniques to find the
maximum number of CDMA channels that can be used with the highest coding rate to
allow for the greatest user bandwidth.
3. SatellitetoControI Station Downlink
The frequency bandwidth allocated for the satellitetocontrol station downlink
is 16.5 MHz from 5150 to 5165.5 MHz. The satellite serves as a relay for the userto
control station data link.
D. POSITION DETERMINATION
After receipt of the time differentials, the central control station computes the co
ordinates of the user from the measured time differentials, and the known location of
each of the satellites.
The x, y. z position determination of the user is defined in a geocentric coordinate
system as shown in Figure 1. The x axis is the intersection of the equatorial plane and
the Greenwich Meridian plane and is oriented from the center of the earth. The y axis
Table 2. NUMBER OF SIMULTANEOUS CDMA CHANNELS WITH FEC
(Hard Decision) at Coded Bit Error probability of IP" 6
Code
Rate
R
1,2
2/3
3/4
4,5
5/6
6/7
7/8
k
1
9
3
4
5
6
7
\ a
36
3
42
12
92
5
9
"free
10
6
5
4
4
3
3
CDMA Channels K
for— j= 100 or 20 dB
247
237
185
172
157
147
145
CDMA Channels K
E h
forrf = 32 or 15 dB
213
204
152
139
124
114
112
completes the cartesian coordinate system with the x axis. The z axis is the north to
south axis connecting the two poles.
Although actual distance is not measured by the user equipment, the distance can
be calculated from the time it took for the other satellites signals to reach the user versus
the first satellite signal that was received. The time differentials are converted to differ
ential distances by multiplying the time differentials by the speed of light (c); approxi
mately 3 x 10 8 m s. The accuracy of the synchronization of the satellites transmissions
plays an important part in the users position determination. If the satellites do not
transmit at the exact same time, the time differentials will not be correct and thus neither
will the distance differentials.
The distance between the unknown user position (x, y, z) and each of the satellites
(.v, j/, 2,) where /= 1, 2, . . ., n can be calculated from
(xxf + ^yf + izzf /= 1, 2,
We further define the distance measurements
a,= d, — d< i= 1, 2. . . ., n
(13)
(14)
Table 3. NUMBER OF SIMULTANEOUS CDMA CHANNELS WITH FEC
(Soft Decision) at Coded Bit Error probability of lO 6
Code
Rate
R
1/2
2/3
3,4
4/5
5/6
6/7
7/8
k
1
2
3
4
5
6
7
**.
36
3
42
12
92
5
9
<7>f<?
10
6
5
4
4
3
3
CDMA Channels K
for^= 100 or 20 dB
400
384
302
281
258
242
238
CDMA Channels K
for r^= 32 or 15 dB
366
351
269
247
225
209
206
as the difference in distance from one satellite designated as satellite one to the user and
the other satellites distance to the user.
For a four satellite case, n = 4, equations (13) and (14) are combined to form four
independent equations and four unknowns, x, y, z, and d v From the known satellite
positions and the time differences which have been measured by the user, the four un
knowns can be solved. Sign ambiguities can be corrected as long as the user knows what
quadrant he is in.
The coordinates of the satellites (x„ y„ z) can be calculated from its longitude
eastward of zero degrees bv
Xi = r cos t
y) = r sin 6
z = Q
(15)
(16)
(IV)
The term z, will remain zero as the satellites are in an equatorial orbit with a latitude of
zero degrees.
Table 4. NUMBER OF SIMULTANEOUS CDMA CHANNELS WITH FEC
(Hard Decision) at Coded Bit Error probability of 10 _ "
Code
Rate
R
1/2
2/3
3/4
4/5
5/6
6/7
7/8
k
1
2
3
4
5
6
7
%,.
36
3
42
12
92
5
9
dfree
10
6
5
4
4
3
3
CDMA Channels K
forrr= 100 or 20 dB
215
200
159
147
135
123
122
CDMA Channels K
for rr=32 or 15 dB
181
167
126
112
102
89
88
The four nonlinear independent equations are
(4  af = (x  xf + [y yf + z 2 i  1, 2, 3, 4
(18)
Equation (18) can be reduced to 3 linear independent equations by substituting equation
(14) into equation (13) and subtracting the (/= 1) equation from the other 3 equations.
The remaining three equations are
2
( Xl x,)x + tv*,J,lv  fl/4 = j f — 2, 3, 4. (19)
The 3 equations can then be entered into matrix form to solve x, y, and d x as shown:
_x A — x } y 4 — J', — a 4
(20)
7 can be calculated by substituting equation (20) into equation (18
Table 5. NUMBER OF SIMULTANEOUS CDMA CHANNELS WITH FEC
(Soft Decision) at Coded Bit Error Probability of 10"'
Code
Rate
R
1/2
2/3
3/4
4/5
5/6
6/7
7/8
k
1
2
3
4
5
6
7
\„
36
3
42
12
92
5
9
"free
10
6
5
4
4
3
3
CDMA Channels K
for~= 100 or 20 dB
349
326
261
239
223
203
201
CDMA Channels K
for tt=32 or 15 dB
316
292
228
206
190
170
168
Z=[(44) 2  (XXf  0'V,) 2 ]2.
(21)
From equation (20) and (21), the user position (x, y, z) can be solved to obtain an initial
approximation. The actual position must be solved iteratively or by utilizing a Kalman
filter. From (x, y, z), the users altitude h, longitude and latitude can be derived.
x = (R + h) cos 6 L cos 9[
y = {R + h) sin L cos 6 {
z = {R + h) sin 0,
(22)
(23)
(24)
where L< d lt and h are solved by
, cos 8 r
xanUz—^)
(25)
(26)
(27)
For a three satellite system, the position solution algorithm is much the same. The
following equation substitutes for the fourth satellite equation
X 2 + y 2 + z 2 = ( R + h ) 2 (28)
As in the four satellite case, these four equations must be solved iteratively to obtain
the users position. In the three satellite case, the user must report his altitude because
only the longitude and latitude of his position can be determined from three satellites.
The four nonlinear equations are
(</,  af = (*  x,) 2 + (yyf + z 2 /= 1, 2, 3 (29)
x 2 +y 2 + z 2 = {R + h) 2 . (30)
As in the four satellite case, the equation with index = 1 is subtracted from the
other two equations.
d x = a x x + B,j + y\ (31)
d x = o. 2 x + B 2 v + y 2 (32)
where
*3 ~ *1
a 2 ' a 2
2.2 2 2.2
*1 + ■>'! ~  Y 2 ~ }'2 + a 2
2a 2
(33)
(34)
(35)
When we solve for y in terms of x, we get
y = H x x + n 2 (36)
where
18
y\  V2 vi  72
B 3 — Bi ' B) — Bi
(37)
The substitution of (36) into (31) produces
d x = m 3 * + ^4 (38)
where
g I B 2 ~ ^2^1 Oigj ~ OgBj ,„.
M3= B 2 5, «• JfcB, ' (39)
The term z 2 can be expressed as
z 2 = rf 2  .r 2 v 2 + lx x x + 2v,j  x\  y]. (40)
Substitution of (36). (38). and (40) into (28) produces
ax 2 + bx + c = (41)
where
a = nl (42)
b = 2n 2 H4 + 2y lf i ] + 2x l (43)
c = ix\ + 2y h u 2  x 2 y 1  (R + h) 2 . (44)
The value of x. y, and z can be calculated from (36), (40). and (41) subject to the
limitation x < 6378 km provided the user knows what quadrant of the earth he is lo
cated in.
E. POSITION ERROR
Even though the satellite is geostationary, the satellite does move about its nominal
position. The drift of the satellite can be calculated to less than 20 meters from its
nominal position. The error that results in the user position determination can be cal
culated. The range error can be expressed as user position error (Ax, Ay, Az.)
cd: dd, 6di
M; = rrAx + r^Ay + r 1  Az
ex cy cz
xx t y\) z
= —  — Ajc 4 —  — Av + — 
d; d, " d;
i= 1, 2, 3, 4.
(45)
Az
Equation (45) can be transformed into matrix form as Av = u and with equation (14),
x ~ x \ y~ y'\ z — 2
4
4
4
x  x 2
y yj
zz 2
d x a 2
d\<h
d\~a 2
x  x 3
yy3
z~*3
d x a 3
d x a 3
X  * 4
yy*
z  z 4
d] — « 4 d x — a 4 rfj — rt 4
(46)
(47)
The user position error can then be simulated by letting the range error be
Ad t = [(.v*',.) 2 + 0/,) 2 + (zz'f'jT
[(xxf + (yyf + (zz,.) 2 ]2
/= 1, 2, 3, 4
where
(.v',, y h z'i) = (x t + Ax h }) + Ay h Zi + Az,).
(48)
(49)
The variable Ad, is the difference between the distance from the user to the nominal
satellite position and the distance from the user to the satellite position that the satellite
may have drifted to. The variables (x'„ y'„ z',) are the coordinates of the nominal satellite
position with the drift distances ( Ax„ Ay„ Az, ) added to the nominal satellite position
coordinates. The error vector v is the linear leastsquares solution of Av = u where
v = {A T A)~ l A T u and the mean squared error is e = {Av — u) T (Av — u). The values
(A.v, Ay, Az) are calculated using Eq. (46) and (47). The error contribution of the z co
ordinate is much less than the x or y coordinate as the user position approaches the
equator. This illconditioned problem results in a poor estimation of Az which can be
minimized by modifying the leastsquares method of solution. By first calculating the
leastsquares estimate of Ax and Ay and ignoring the Az component of the total error
and calculating Az after Ajc and Ay are found, a better estimate of the total error can be
found.
' A,) A
Az = {A 2 A 2 )~ l {A[u  A%A x v x )
(50)
(51)
where
A, =
4
d\
x — x 2
y
— y 2
d ] — a 2
d\
~ a 7
x  x 3
y
4
~ }'3
d \  «3
~ «3
V — X A
y
 J"4
d\ ~ a A
(52)
d\
z

z 2
dx
~
a 2
z

z 3
4

«3
z

^
(53)
For a three satellite system, the range errors Ad, /= 1, 2, 3 are calculated from
equation (45) and the user altitude error Ah is calculated from equation (30) as
Ah
x(Ax) + y(Ay) + z(Az)
[x 2 + / + z 2 ]l
x(Ax) + y(Ay) + z(Az)
R + h
(54)
The user position error vector v = [Ax, Ay, Az~] T is the leastsquares solution of
Bv = w which is v = (B T £)' B T w , where
x  x ] y  y\ z  z ]
d \ d \ d \
x ~ x 2 y  y 2 z  z 2
d ] — a 2 d x — a 2 d^ — a 2
x ~ x 2 y  y 3 z  z 3
d \ ~ a 3 d\ ~ a 3 d \ ~ a 3
(55)
R + h R + h R + h
Tor the three satellite case, the leastsquares method is also modified to provide a better
estimate of v. The variable v is calculated from v = [v,. Azl r where
Az = (B[ B 2 )~ l (B[ w  B 2 T B ]V] )
(56)
(57)
and
x  *i y  y\
d x
dx
X
~ x 2
y — >'2
dx
~ a i
dx ~ "2
X
~ x 3
y  >3
dx
 a 3
X
dx  «3
y
R + h R + h
dx
z

*2
d\

<*2
z

z 3
dx
;
«3
R + h
(58)
Equations (50), (51), (56), and (57) calculate the upper limit of the error in the user
position provided the satellites position errors are known in either the three of four sat
ellite case. The average error for various users positions has been compiled in [Ref. 1].
The average error in the users position increases as the user approaches the equator.
The average error ranges from 14.2 to 61.5 meters depending on how close to the
equator the user is. The closer the user is to the equator, the worse the error which in
dicates a weakness in the system.
F. CONTROL STATIONTOUSER DATA LINK
1. Uplink Bandwidth
The frequency bandwidth allocated for the control stationtosatellite uplink is
6524.5 to 6530.77 MHz. The 6.27 MHz bandwidth coincides with the available band
width of the satellitetouser downlink part of the relay.
After the control station has completed the calculations and the user position
is determined, the position coordinates have to be sent to the user. A TDM channel is
used to transport the user information to the user. To calculate the total carriertonoise
density ratio of the control stationtouser link. Eqs. (5)  (8) are used as was discussed
in the usertocontrol link.
The uplink frequency is 6533 MHz with an antenna gain (G,) of 44.5 dB. which
is a standard antenna gain for a ground station antenna. The antenna gain is much
higher than for a mobile vehicle as one is able to use a large dish. The power out (/>,)
is set at only 1 watt per channnel since there would be more than one channel simul
taneously transmitted by the control station. For example, if 200 CDMA channels were
used, then 200 watts of power would be required for transmission of the channels. The
lower power out is standard for a ground station. For this link design, the satellite G T
is 1.5 dB K. The power out and the satellite G,'T values are design parameters deter
mined by judgement and current systems. For the control stationtouser link, the total
carriertonoise density ratio is 66.25 dBHz is calculated by Eq. (8). A carriertonoise
density ratio of 66.25 dBHz is sufficient for a successful link. A 5 dB margin is engi
neered into the system to allow for the crossinterference degradation of the system by
the multiple carriers that are transmitted by the control station. After subtracting the
5 dB margin from the total carriertonoise density ratio, converting to a factor and di
viding the result by the required noise ratio factor, the data rate for the bit error proba
bilities of 10" 6 and 10" are 42.2 kbps and 13.3 kbps, respectively. The calculations for
the control stationtouser link utilize Eqs. (5)  (8), which have been discussed earlier.
These are the same equations as Table 1 with only the input values differing. The con
trol stationtouser link analysis is tabulated in Table 6.
Table 6. SYSTEM I CONTROL STATIONTOUSER LINK ANALYSIS
Uplink Frequency
6533 MHz
Antenna Gain
44.5 dB
Transmitted Power
1 W
Carrier EIRP
44.5 dBW
Free Space Path Loss
199 dB
Satellite G/T
1.5 dB K
Boltzmann's Constant
22S.6 dBW/KHz
Uplink
CarriertoNoise
Density Ratio
72.6 dBHz
Downlink Frequency
2491 MHz
Satellite EIRP
53.6 dBW
Free Space Path Loss
191 dB
User G T
23. S dB K
Downlink
CarriertoNoise
Density Ratio
67.4dBIlz
Total
CarriertoNoise
Density Ratio
66.25 dBHz
Margin
5 dB
If Required rf =
15 dB
20 dB
Then Data Rate can be
42.2 kbps
13.3 kbps
2. Control StationtoUser Data
Using the available data bit rate, the user coordinates, identification tag and
synchronization bits must be transmitted to each user that has requested a position fix.
There are 58 bits required to represent the latitude, longitude, and altitude. Seven bits
are allowed for degrees (where 2" =128 which will suffice to represent the users position
if the user supplies to his machine the quadrant that he is in). There are 6 bits for min
utes, and 6 bits for seconds, where 2 6 = 64 will suffice to represent 60 values for both
latitude and longitude. Another 20 bits are required to represent the user altitude. In
Figure 3, a 40 bit code word is used for synchronization of the TDM frame. A 40 bit
code word is a design parameter which is used in other communication systems. Each
user information frame consists of two 8 bit flags, position information of 58 bits, gen
eral information of 20 bits and a user ID of 10 bits. The 8 bit flags provide the start and
end of the user data.
SYNC
USER 1
USER 2
USER N
1
FLAG
ID
POSITION
DATA
GENERAL
DATA
FLAG
Figure 4. TDM Frame (Control Station to Users)
3. SatellitetoUser Downlink
The data link from the control station to the user is completed with the
satellitetouser downlink at a frequency bandwidth of C.27 MHz between 2493.73 MHz
and 2500 MHz. The satellite provides relay service only and does not process the data
that is passed through.
III. SYSTEM II
A. SYSTEM II DESCRIPTION
System II will employ 3 or 4 satellites in the same arrangement and positions as
System I. System II differs from System I in the technique by which the differential
distances are obtained. System II users will transmit a user unique pseudorandom
ranging code to the control station via a satellite relay. The time delays between the ar
rivals of the codes from each of the satellites will determine the differential distances of
the paths. Each time the user transmits a code, the code will travel to the satellites at
the speed of light. The satellite that is closest will receive the code first and relay the
code to the central control station. The closest satellite will provide the shortest time
delay. The satellite that is furthest away from the user and the central control station
will have the longest delay. It is these differences in the times of arrivals that determine
the distance differentials as we did in System I. In System II, a total usertosatellite and
satellitetocontrol station differential distance is calculated from the total time differen
tial. The centra] control station assumes the task of measuring the differences in the
round trip distance between itself and the user via one satellite, arbitrarily designated as
satellite one. and each of the other satellites. We define these differential distances as
^■ = (/ 1 +^)( / / + 4). i=l,2 f ...,/i (59)
where / is the distance from the central control station to the satellite
if = (x  xf + Oo j,,.) 2 + (z  zf, / = 1, 2, ..., n (60)
and d, is the distance from the user to the satellite
dj = {x  xf + (y yf + (z zf, i 1, 2, ..., n (61)
For n = 4, Eqs. (9)  (11) combine to form a set of four independent equations and
four unknowns, namely, x, y, z, and d x These four equations are
(4  *, + /,  if  (x  xf + (yytf + (z  zf, /= 1,2,3,4 (62)
For n = 3. Eq. (4) is used in addition to Eq. (12) for /= 1, 2, 3 assuming the user
altitude h is known.
After the position solution is obtained, the control station relays the user position
to the user via a satellite link as in System I. The frequency assignment and bandwidth
allocated for each of the satellite links listed below are specified by the Federal Com
munications Commission in [Ref. 2].
• UsertoControl Station
UsertoSatellite Uplink
Frequency 1610  1626.5 MHz
Bandwidth 16.5 MHz
SatellitetoControl Station Downlink
Frequency 5150  5166.5 MHz
Bandwidth 16.5 MHz
• Control StationtoUser
Control StationtoSatellite Uplink
Frequency 6524.5  6541 MHz
Bandwidth 16.5 MHz
Satelliteto User Downlink
Frequency 2483.5  2500 MHz
Bandwidth 16.5 MHz
• Control StationtoSatellite Command Link
Frequency 6526.5  6541.5 MHz
Bandwidth 15 MHz
B. USERTOCONTROL STATION LINK
1. Uplink Bandwidth
The frequency bandwidth allocated for the usertocontrol station data link is
16.5 MHz from 1610 MHz to 1626.5 MHz. Within this bandwidth, the user must
transmit a PN ranging code, an identification code, general information, and user alti
tude in the three satellite configuration. The user will transmit a standard navigation
1,023 chip Gold code sequence as the ranging code with the other data. The calculations
for the usertocontrol station are completed as was discussed in System I, utilizing Eqs.
(5)  (8). System II design parameters are the same as System I. The total carrierto
noise ratio less the 2 dB margin will support data rates of 57 kbps and 18 kbps for re
quired signaltonoise ratios of 15 dB and 20 dB, respectively. The link analysis is
tabulated in Table 7.
2. UsertoControl Station Data
As in System I. the user must transmit a 10 to 17 bit user identification number, 20 bits
for additional information, and 20 bits for altitude if only three satellites are used. Using
a standard modulation scheme, this information would be modulated by QPSK and
Table 7. SYSTEM II USERTOCONTROL STATION LINK ANALYSIS
Uplink Frequency
1618 MHz
Antenna Gain
4dB
Transmitted Power
SOW
Carrier EIRP
23 dBW
Free Space Path Loss
190 dB
Satellite G T
+ 3 dB K
Boltzmann's Constant
228.6 dBW KHz
Uplink
CarriertoNoise
Density Ratio
64.6 dBHz
Downlink Frequency
5150 MHz
Satellite EIRP
36 dBW
Free Space Path Loss
19S dB
Control Station G/T
20 dB K
Downlink
CarriertoNoise
Density Ratio
86.6 dBHz
Total
CarriertoNoise
Density Ratio
64.57 dBHz
Margin
2dB
If Required rr =
15 dB
20 dB
Then Data Rate can be
57 kbps
18 kbps
spread with the 1023 chip Gold code. The number of CDMA channels that the system
will support is the same as in System I.
3. SatellitetoControl Station Downlink
The frequency bandwidth allocated for the satellitetocontrol station downlink
of the usertocontrol station data link is 16.5 MHz from 5150 to 5165.5 MHz. The
satellite functions as a relay onlv as in Svstem I.
C. POSITION DETERMINATION
The position of the user is determined in much the same manner as was done in the
System I design. The main difference is that there are two distances that must be ac
counted for in the calculation. In System I, the satellites transmit the ranging code and
the differential distances between the satellite and the user had to be accounted for in
position error. In System II, the user transmits the code so the usertosatellite and
satellitetocontrol station differential distances must be taken into consideration when
calculating the users position. The differential distance measurements are made using
Eq. (59).
The central control stationtosatellite differential distance error does not contribute
to the user position error as greatly as do the satellitetouser distance differentials. The
central control station would be suitably located away from the equator to minimize the
control stationtosatellite differential distance measurement errors that are inherent to
the system as was discussed in System I. In the three satellite configuration, where al
titude must be entered for position determination, the central control station knows its
exact altitude, so the only altitude error entering into the position determination is from
the user. In the four satellite configuration, satellite position errors between the user
tosatellite and central control stationtosatellite do increase the user position error but
not as greatly as first thought. After conducting a computer simulation model run of
1000 iterations with randomly varying satellite position errors between + 20 and  20
meters as was conducted m [Ref. I]; approximately a 1 to 2 meter additional error was
added to the overall position error of System II in comparison with System I user posi
tion error. It was originally thought that a doubling of the position error would occur
since an error in the satellite position affects both the usertosatellite and the central
control stationtosatellite paths, but was not the case. For this reason, the System II
design is a viable alternative to System I design.
D. CONTROL STATIONTOUSER DATA LINK
1. Uplink Bandwidth
The System II control stationtouser data link is designed the same as the data
link in System I. The big advantage in System II is that the bandwidth allocated for the
satellitetouser downlink is used solely for the control station to user data link. The
total bandwidth of 16.5 MHz can be utilized for data transmission because there is no
ranging code to be transmitted by the satellites. In System I, the ranging code occupied
10.23 MHz of the 16.5 MHz bandwidth allocated for the satellite to user link, leaving
onlv 6.27 MHz for the control stationtouser data link.
2. Control StationtoUser Data
As in System I. the user ID, latitude, longitude, altitude and general information must
be transmitted to the user. The System I TDM frame structure will also be utilized in
System II. In System II, the number of users that can be serviced each second could
be increased even further due to the 10.23 MHz increase in the available bandwidth.
The increase in the number of users will depend on the protocols used and is beyond the
scope of this thesis. The link calculations are completed using Eqs. (5)  (8) and System
I link parameters. The values obtained in Table 8 are identical to those in System I for
the same link parameters. Table 8 is furnished to present the fact that the link calcu
lations do not change.
3. Satellite to User Downlink
The satellite to user downlink occupies the full bandwidth of 16.5 MHz from
1610 to 1626.5 MHz. The satellite operates as a passive relay only.
Table 8. SYSTEM II CONTROL STATIONTOUSER LINK ANALYSIS
Uplink Frequency
6533 MHz
Antenna Gain
44.5 dB
Transmitted Power
1 W
Carrier EI RP
44.5 dBW
Free Space Path Loss
199 dB
Satellite G T
1.5 dB K
Boltzmann's Constant
228.6 dBW; KHz
Uplink.
CarriertoNoise
Density Ratio
72.6 dBHz
Downlink Frequency
2491 MHz
Satellite EIRP
53.6 dBW
Free Space Path Loss
191 dB
UserG T
23.8 dB K
Downlink
CarriertoNoise
Density Ratio
66.25 dBHz
Total
CarriertoNoise
Density Ratio
61.73 dBHz
Margin
5dB
If Required 77 =
15 dB
20 dB
Then Data Rate can be
42.2 kbps
13.3 kbps
IV. SYSTEM COMPARISONS AND CONCLUSIONS
System II is the simpler system in many ways. A System II user sends the ranging
code to the control station so the time of transmission does not require any synchroni
zation. The satellite does not require an onboard clock or a code generator and trans
ponder to send a ranging code to the user. There exists the possibility of using existing
satellites or sharing future satellites. The user equipment is also simpler in that the user
does not have to make time measurements of the satellitetouser time differentials. By
reducing the complexity of the user equipment, the cost to each user would also be re
duced.
The number of users that could simultaneously be serviced by System II is also
greater because the available bandwidth of the control station to user is dedicated totally
to the link. In System I. the satellitetouser bandwidth must also support the trans
mission of the ranging code from the satellite to the user reducing the bandwidth of the
control stationtouser link. Although there is a slight increase in position error that is
inherent to System II, the position accuracy is well within expected tolerances required
of many civilian users.
This thesis has proposed the concepts of two Global Satellite Location and Tracking
Systems designed for the civilian user. The advantages of the systems are the low cost,
user equipment simplicity, and accurate position determination. The user systems are
cheaper because the computational hardware and software are maintained at the central
control station. This eliminates the need for installing an expensive computer in each
user transceiver.
System II provides many possibilities for future design due to the fact that satellites
already in space could be used as communications relays for the system. This eliminates
the need to design and launch special satellites into space for location and tracking
purposes only.
Geostationary Satellite Location and Tracking Systems are viable systems for civil
ian position determination.
V. LIST OF REFERENCES
1. Ha, Tri T. and Robertson, R. Clark, Geostationary Satellite Navigation Systems,
IEEE Transactions on Aerospace and Electronic Systems, Vol. AES23, NO. 2,
Pages 247  254, March 1987.
2. Manual of Regulations and Procedures for Federal Radio Frequency Management ; 3
December 1985.
3. Ha, Tri T., Digital Satellite Communications, McMillan Publishing Company, 1986.
4. Spilker, James J. Jr., Digital Communications by Satellite, PrenticeHall Inc., 1977.
5. Shu Lin and J. Costello Jr., Error Control Coding: Fundamentals & Applications,
PrenticeHall, Inc., 1983.
6. Thomas C. Bartee / Editor, Data Communications, Networks, and Systems, Howard
W. Sams & Co.. 1985.
VI. INITIAL DISTRIBUTION LIST
No. Copies
1. Defense Technical Information Center 2
Cameron Station
Alexandria, VA 223046145
2. Library, Code 0142 2
Naval Postgraduate School
Monterey, CA 939435002
3. Department Chairman. Code 62 1
Department of Electrical and Computer Engineering
Naval Postgraduate School
Monterey, California 939435000
4. Professor Tri T. Ha, Code 62Ha 5
Department of Electrical and Computer Engineering
Naval Postgraduate School
Monterey, California 939435000
5. Professor Glen A. Myers, Code 62Mv 2
Department of Electrical and Computer Engineering
Naval Postgraduate School
Monterey. California 939435000
6. Commander 1
Naval Space Command
ATTN: Code N3
Dahlgren, Virginia 22448
7. Commander 1
United States Space Command
ATTN: Technical Library
Peterson Air Force Base, Colorado 80914
8. Chief of Naval Operations 1
ATTN: Naval Space Division (OP943)
Washington, DC 203052000
9. MR. Roger Casey 1
Naval Ocean System Center
ATTN: Code 805
San Diego, California 921525000
10. Major Danny L. DeFries 3
ATTN: Science and Technology Center, EUROPE
APO NY 09079
n/
Thesis
D2443
DeFries
c.l
Inexpensive global lo
cation and tracking sys
tems using geostationary
satellites.
luesis
D2443
c.l
DeFries
Inexpensive global lo
cation and tracking sys
tems using geostationary
satellites.